Yeah. I was thinking it doesn't have to be a city map. Could be continent outlines, or...

There's a video from Gnomon where Scott Robertson scribbles with grey Prismacolors on some vellum and then scans them in, collages them together, and paints some very cool landscapes from the shapes suggested by the collages. Might be something there for mapping as well, or...

You could pack up a collection of brushes, patterns, etc. and have people build something from them. Might get some interesting surprises from a grab-bag mapping challenge. I've seen something similar done with modeling (physical) where folks get a box of parts and have to build something.

So many possibilities...too bad we have to work.
M